Assessment of Surface Water -Groundwater Relationship in the Area Between Borg El Arab and West El Hammam, North West Coastal Zone, Egypt

The study area, between Borg El Arab and El Hammam, is recently subjected to intensive land reclamation projects aiming to cultivate about 57000 feddans. It is supplied by two main sources of irrigation, i.e. the surface water as a main source (Bahig canal and El Hammam canal), and the groundwater from more than 600 shallow wells tapping the Ralat aquifer (calcareous sandstone) of Plio-Pleistocene age as a supplement source. During the last three decades (1985 – 2014), conjunctive use of surface water together with groundwater has resulted in serious hydrologic problems e.g. water losses, canal seepage and water logging, where the depth to water level has risen up from about 20 m (1985) to less than 5.0 m (2014). Meanwhile, the groundwater salinity decreased during this period from more than 5000 ppm to less than 2000 ppm, indicating a dilution effect by seeped water. The water seepage from the dissecting canals is estimated in the present work by 65.18 x 106 m3/year replenishing the groundwater system in the down gradient areas. Might as well, the irrigation return flow through permeable soil in the study area is estimated by 4.125 x 106 m3/year due to the applied flood irrigation technique. In other words, 95% of the total groundwater replenishment is from the canal seepage, while only 5% from direct percolation. The investigation of wells tapping the Ralat aquifer in the study area has indicated that water levels are ranging from 21.0 m to 1.0 m above mean sea level. More than 57.6 x 106 m3/year (average 84% of the natural groundwater discharge) are pumping from such wells to get water of about 2000 ppm salinity, indicating a significant hydraulic connection between the surface water canals and the underlying aquifer. The calculated water balance of the Ralat aquifer has resulted in an amount of annual surplus water of the order of 11.705 x 106 m3/year as groundwater storage.